The present invention relates generally to the art of skin treatment using electromagnetic radiation. More particularly, the invention relates to an efficient method and apparatus for skin rejuvenation by ablation of the outer layer of the skin and wrinkle smoothing (or shrinking) by heating of collagen without damage to the epidermis.
There is a strong desire today to obtain and/or maintain a youthful appearance. One manner of doing so is to remove (or reduce) wrinkles. Additionally, it is desirable to rejuvenate the skin by removing an outer layer of skin. There are known techniques for removing wrinkles by peeling the skin. Also, there are known methods for rejuvenating the skin. Unfortunately, all known techniques suffer from lack of efficacy and risk to the patient.
One known method of skin rejuvenation includes injection of collagen underneath the skin. This has been performed using a bovine collagen injection. For example, microfine collagen has been injected into periocular lines. Some of the problems with collagen injection include allergy to collagen and lack of longevity. Also, often there is only partial eradication of the wrinkles.
Peeling most or all of the outer layer of the skin is another known method of rejuvenating the skin. Peeling can be achieved chemically, mechanically or photothermally. Chemical peeling is often carried out using trichloroacetic acid and phenol. An inability to control the depth of the peeling, possible pigmentary change and risk of scarring are among the problems associated with chemical peeling.
The mechanical method is called transcutaneous blepharoplasty and involves shaving off the outer layer of skin. Skin resection during lower lid blepharoplasty frequently results in undesirable side effects, especially ectropion and scleral show. Moreover, transcutaneous blepharoplasty rarely eradicates all of the wrinkle lines.
Pulsed carbon dioxide laser treatment is a known photothermal method of removing of periocular wrinkles. However, laser light is heavily absorbed in water and has a very short range in the epidermis. Thus, a high fluence with short pulse durations will evaporate the outer layer of the skin and peels most or all of the epidermis and simultaneously heat deeper skin layers that cause collagen shrinkage.
The use of CO2 laser light for skin rejuvenation also has undesirable side effects. For example, CO2 lasers have small spot size (3 mm or less), and thus their use causes valleys and ridges, particularly when resurfacing large areas. Also, it is difficult to control heat diffusion, and thus the resultant necrosis is difficult to predict and control. Additionally, scar tissue absorbs CO2 laser light differently than normal skin and thus may adversely impact such a treatment.
Another known method of skin peeling uses an Er:Yag laser. The small penetration depth of the Er:Yag laser enables removing of the outer layer of the skin without causing collagen heating. A treatment of that kind helps the skin to look younger, but does not help to smooth deep wrinkles.
Thus, it is apparent there is a need for a new method and device with which it is possible to produce efficient wrinkle removal and skin rejuvenation. This apparatus would preferably be able to control the treatment parameters according to characteristics of the tissue, and be easily tunable. The new method and device would preferably provide efficient wrinkle smoothing and skin rejuvenation without removing outer skin layers and with minimal side effects.
In accordance with one aspect of the invention there is provided a method and apparatus for treating skin including applying pulsed light to the skin for heating and shrinking collagen within the skin, thereby reviving the elasticity of the collagen and of the skin. In one embodiment the method also includes protecting the epidermis and outer layers of the skin by cooling the epidermis and outer layers of the skin. The cooling may be accomplished by applying a cooled transparent substance, such as ice, gel or crystal, to the skin.
In one alternative embodiment the skin is cooled by first applying the transparent substance to the skin and then cooling it.
In another alternative embodiment the temperature distribution within the skin is controlled by controlling the delay between the time the coolant is applied, and the time the light is applied. A microprocessor may be used for determining the delay time in response to a selected skin temperature profile. Additionally, the temperature distribution may be controlled by controlling the pulse duration and applying multiple pulses. In another embodiment the temperature distribution within the skin is controlled by filtering the light and controlling the radiation spectrum. Preferably, the spectrum includes light having a wavelength in the range of 600-1600 nm.
In another embodiment the pulsed light may be incoherent, such as that produced by a flashlamp, or coherent, such as that produced by an Nd(Yag) laser, an Alexandrite laser, a Diode laser, an Er:glass laser or a ruby laser.
In another embodiment the light is directed to the skin using a flexible or rigid light guide.
In accordance with a second aspect of the invention there is provided a method and apparatus for generating a temperature distribution inside a region of skin having a maximum temperature at a selected depth including cooling the epidermis and outer layers of the skin and applying pulsed light to the skin.
In one embodiment the cooling is accomplished by applying a cooled transparent substance, such as gel, ice or crystal, to the skin. Alternatively, the cooling may be accomplished by first applying the transparent substance, and then cooling it.
The temperature distribution is further controlled in one embodiment by controlling the delay between the cooling and the light application. In another embodiment the distribution is controlled by controlling the pulse duration and/or applying multiple pulses.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.